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MIG 7 Series - Receiving ERROR: [Drc 23-20] when CLOCK_DEDICATED_ROUTE set to BACKBONE but the backbone resources are not used

Description

For designs that previously generated a bit file successfully in 2013.4, you may now receive the following error related to the BACKBONE routing even though the CLOCK_DEDICATED_ROUTE constraint is applied correctly:

ERROR: [Drc 23-20] Rule violation (RTRES-1) Backbone resources - 1 net(s) have CLOCK_DEDICATED_ROUTE set to BACKBONE but do not use backbone resources. The problem net(s) are clk_in1.

Solution

This issue can occur for some designs where SYS_CLK is not within the same bank as the MIG interface.

For example, 2 MIG interfaces sharing one SYS_CLK or 1 MIG interface where the SYS_CLK is in a different bank.

A conflict can occur when, the design is routing which, causes the net assigned to the backbone, not to be able to get onto the backbone routing and as such the DRC received is correct.

However, this is still an issue as the tools should be able to handle this configuration.

Note: The routing was incorrect in previous SW versions as well, the DRC is new in 2014.1.

This workaround would also be required with release 2013.4 and prior.

To check whether your net has been correctly placed on the backbone in previous SW versions where the DRC is not flagged, customers can run the following command on an open implemented design.

It is clear that no Backbone has been used as in the route properties you should see "BB" used, see the below workaround for an example of a working route.

There is a workaround available for this issue, which is to directly apply a routing property to the net requiring the backbone routing.

The steps below show how this can be achieved:

Open the implemented design and from the Tcl console perform the following:

report_drc -file pre_wa_drc_chk.rpt

This performs a DRC check and shows the DRC reported by write_bitstream.

route_design -unroute

Unroutes the entire design.

route_design -nets [get_nets clk_in1]

Routes the net reported in the DRC error only.

set_property IS_ROUTE_FIXED 1 [get_nets clk_in1]

Locks the net.

route_design

Routes the rest of the design.

report_drc -file post_wa_drc_chk.rpt

DRC error no longer reported.

Now you will need to create a route constraint to add to the XDC file to ensure that the tools will successfully route the design and that this clk net will be placed on the backbone routing as required.